In this study we describe an effective and reproducible method of injecting polidocanol, a foamed sclerosant drug, in the aqueous humor outflow pathway, to induce a moderate and persistent elevated intraocular pressure (IOP) and optic nerve damage in rats.

Methods

Unilateral elevation of IOP was produced by polidocanol injection into perilimbal veins in adult NMRI rats using 10 μl borosilicate glass micropipettes made with a P-97 Flaming/ Brown Micropipette puller. After rats were anesthesized by isoflurane inhalation, the conjunctive was carefully dissected and perilimbal veins were exposed. Polidocanol was slowly injected in the limbal vascular plexus with a force just enough to blanch the perilimbal vessels. IOP was measured every other day in both eyes using a tonometer TonoLab (Icare), as previously described and conducted consistently at the same time. Optic nerve and retina functional and structural damage were assessed with full-field scotopic and pattern ERGs, Optical Coherence Tomography (OCT) and Brn3A Inmunohistochemistry in flat-mounted retina preparations and standardized automated retinal ganglion cell (RGC) counts.

Results

A single injection of perilimbal polidocanol induced IOP elevation up to four weeks, without causing overt ocular structure damage or inflammatory responses while inducing RGC and axon degeneration that simulated glaucomatous changes. Among experimental eyes, the group average IOP (± SD) was 23 ± 6.6 mmHg whereas for control eyes was 12.1 ± 1.4 mmHg (t=3.7, P<0.02) under isoflurane anesthesia. There was a selective reduction of the pattern ERG whereas other ERG components remained unaltered indicating no damage to the outer retina. RGC functional injury occurred before the onset of structural damage, as assessed by light microscopy. Significant reductions of RGC number and densities were noted in the experimental eyes compared with the contralateral control eyes, as revealed by OCT and BR3nA retrograde labeling.

Conclusions

This new experimental rat model shows a moderate and consistnet increased IOP, death of RGC but not other retinal neurons, lack of adverse effects on the cornea and sclera and low-cost of implementation.